Vehicle antenna for vehicular communication system using leaky coaxial cable

ABSTRACT

A vehicle wireless communication system utilizing a leaky coaxial cable installed along the vehicle track and having an array of slots in its outer conductor. A coaxial type antenna is mounted aboard a vehicle traveling on the track. The outer conductor of the coaxial type antenna is provided with an array of slots in the axial direction which substantially coincides with the array of slots in the leaky coaxial cable with respect to slot structure and cycle of slot arrangement. A dielectric material is interposed between the inner and outer conductors of the antenna and is adjustable to equalize the wavelength contraction ratio of the antenna to that of the leaky coaxial cable.

United States Patent 1 1 Nakahara et al.

VEHICLE ANTENNA FOR VEHICULAR COMMUNICATION SYSTEM USING LEAKY COAXIAL CABLE Inventors: Tsuneo Nakahara; lliroshi Kitani; Kenlchi Yoshlda, all of Osaka. Japan Assignee: Sumitomo Electric Industries, Ltd.,

Osaka, Japan Filed: Jan. 20, 1971 Appl No.: 108,071

US. Cl ..343/7l3, 343/771, 333/84 R int. Cl. .mn 13/10 Field of Search ..343/770, 771, 7l 3;

References Cited UNITED STATES PATENTS 3/1972 Nakahara etal. ..,..a25/s| 12/1971 Babaetal .325/53 [451 Apr. 24, 1973 7/1962 Butler ..343/77| 2,573,746

ll/l95l Watson et Primary ExaminerEli Lieberman Auomey--Carothers and Carothers S 7 ABSTRACT A vehicle wireless communication system utilizing a leaky coaxial cable installed along the vehicle track and having an array of slots in its outer conductor. A coaxial type antenna is mounted aboard a vehicle traveling on the track. The outer conductor of the coaxial type antenna is provided with an array of slots in the axial direction which substantially coincides with the array of slots in the leaky coaxial cable with respect to slot structure and cycle of slot arrangement.

A dielectric material is interposed between the inner and outer conductors of the antenna and is adjustable to equalize the wavelength contraction ratio of the antenna to that of the leaky coaxial cable.

4 Claims, 9 Drawing Figures Patented April 24, 1973 3,729,740

2 Sheets-Sheet 1 ELgJa.

/N vsuroes. 7Isuua Amara/Men, H/EOSH/ K/r N, 4 KEN/(HI YOSH IDA THE/E A TTOZA/E Y5 (h/eorHsksaqka-maes VEHICLE ANTENNA FOR VEHICULAR COMMUNICATION SYSTEM USING LEAKY COAXIAL CABLE BACKGROUND OF THE INVENTION a. Field of the Invention The invention relates in general to antennas and in particular to leaky antennas for a wireless vehicular communication and control system using a leaky coaxi- SUMMARY OF THE INVENTION The present invention comprises a vehicle antenna made of a coaxial line whose outer conductor has slots periodically arranged along the axis of said line.

The ratio of the waveguide wavelength to the freespace wavelength and slot arrangement of said antenna are made to be in accord with those of the leaky coaxial cable in use. Therefore, the radiation property of the antenna is made quite the same as that of a leaky coaxial cable, and thereby satisfies the basic conditions required for a vehicle antenna in a vehicular communication system using a leaky coaxial cable. The shape of the antenna may be circular, rectangular or a strip-state coaxial line.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1(a) and 1(1)) are diagrams showing the directivity required of an antenna used for a leaky coaxial cable.

FIG. 2 is a perspective view of a leaky coaxial cable with zigzag slots.

FIG. 3(a) is a perspective view showing the construction of an antenna according to this invention. FIG. 3(b) is a perspective view showing a connector for the antenna shown in FIG. 3(a).

FIG. 4(a) and FIG. 5 are perspective views showing other embodiments of the construction of an antenna according to this invention. FIG. 4(b) is a perspective view showing a connector for the antenna of FIG. 4(a).

FIG. 6 is a diagrammic plan view showing the relative positioning of the leaky coaxial cable and the antenna.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a directivity pattern of vehicle antenna used in conbination with a leaky coaxial cable, as well as the directivity pattern of said cable. In the figure, 1 denotes a leaky coaxial cable, 2 a directivity pattern of waves leaked from said cable, 3 a vehicle antenna on board a vehicle, and 4 a directivity pattern of said antenna. The directivity 4 of a vehicle antenna is basically made to be in accord with the directivity 2 of the leaked wave of the leaky coaxial cable, throughout the whole frequency range in use, in order to realize the desired coupling between said antenna and cable. Furthermore, the coupling loss, which is defined as the ratio of the transmitting power inside the cable to the received coupling power by a vehicle antenna, is a very important value in constructing a vehicular communication system, and it is desirable that the coupling loss be made to be as small as possible. Furthermore, it is basically required that a vehicle antenna should be of a simple construction and easy to handle for maintenance purposes, because it is mounted on board a vehicle.

A leaky coaxial cable is recognized as one of the best suitable transmission lines for a vehicular communication system and especially inside a tunnel and under the ground. This is so because the cable can produce a uniform distribution of an electromagnetic wave, which is leaked out through its slot array in the outer conductor, along the cable axis.

FIG. 2 shows a typical example of a slot array for leaky coaxial cables wherein the array is cut in the outer conductor. In the figure, 5,, 5 designated slots, and 6 the outer conductor. The slot array is characterized by its zigzag arrangement of two kinds of straight slots in the outer conductor. Each different kind of slot is located periodically along the cable axis at a slot pitch p, which is designed to be nearly equal to one waveguide wavelength, so as to leak one principal leaky wave to external space along the cable. Two different types of slots are arranged alternately at a slot spacing of P/2. In such a periodical structure of slots, when a transmitter is connected to the left side of the cable in FIG. 2, the directivity of the leaky wave is indicated to be in the O-direction as shown in the figure. The following equation gives the theoretical relationship between the angle 0 of directivity, the ratio 11 of waveguide wavelength to the free space wavelength, the pitch p of slots, and the free space wavelength A in use.

flcos 1/1 n A/p), n: integer 1 According to Eq. 1 the angle 6 is decided by the ratio 11 of the waveguide wavelength, the pitch p of the slots and the wavelength A in use. In other words, when 1/ and p of a slot antenna is taken to be the same as said cable, it becomes possible to obtain the same directivity as said cable, over the whole frequency band in use. Eq. l) is valid for the leaky coaxial cable in the same manner.

FIG. 3(a) shows the first example embodiment of the present invention. In the figure, 7 indicates an inner conductor and, 8 an outer conductor separated from the inner conductor by a dielectric insulator. In the outer conductor 8, straight slots 10,, 10 are periodically located in a zigzag pattern along the'axis of coaxial line. The configulation and the pitch of these slots are made to be in accord with those of a leaky coaxial cable. FIG. 3(a) illustrates the slot array in a zigzag fashion as one example of slot configuration.

. These slots may be made to other co'nfigulations or forms in accord with the leaky coaxial cable in use. The pitch p of the slots and the ratio 1/ of the waveguide wavelength to the free space wavelength of an antenna of this invention are made just the same as those of a leaky coaxial cable in use. Under such conditions, the antenna can obtain the same property of directivity as the leaky coaxial cable in use, owing to the relation of Eq. l The ratio 1 of the waveguide wavelength to the free space wavelength (wavelength contraction ratio) of said antenna is adjusted to the same value of the cable by varying the ratio of occupation of the insulator between the outer conductor 8 and inner conductor 7.

The present invention has the simple structure of a coaxial line whose outer conductor has a slot array along the coaxial line, and it can be easily operated by feeding power at the one end of the antenna. The antenna of the present invention can obtain perfect beam matching with a leaky coaxial cable installed in parallel. Furthermore, this antenna can obtain a high gain and realize stable communication by reducing the fluctuation of the coupling loss, since it covers a wide region of radiation from said cable along its axis, as the antenna can be easily made as a long antenna. According to the results of experiments actually conducted with a 6-meter length antenna of the present invention, the antenna gain was improved by about l dB, as compared to a standard dipole antenna, and the fluctuation of the coupling level with the cable was about $0.5 dB. A great improvement was thus obtained if compared with the fluctuation of i 2.5 dB or more observed when receiving signals by a standard dipole antenna.

FIG. 4 shows another embodiment of the antenna of this invention. The afore-mentioned antenna (See FIG. 3.) made of a coaxial tube is here replaced by a coaxial line having a rectangular cross section. In the Figure, 7 denotes an inner conductor consisting of a narrow strip, 8 an outer conductor having a rectangular cross section, and 9 a dielectric material for the purpose of regulating the wavelength contraction ratio of the antenna, which at the same time serves the purpose of fixing and supporting the inner conductor 7.

Generally speaking, it is preferred if the outer conductor 8 is shaped to have a flat cross section and to have a broad face confronting the leaky coaxial cable. It is not particularly necessary to make its cross section rectangular. It is also preferred to provide an outer conductor fin shown as 12 in the Figure, 10,, denote slots provided on the broad wall of the outer conductor which faces the leaky coaxial cable. As an example, such slots are in conformity with the slot structure of a leaky coaxial cable with zigzag slots. Just as in the case of the embodiment of FIG. 3 the slot structure of this antenna is required to be in conformity with the slot structure of the leaky coaxial cable to be used. it is not always necessary to use zigzag slots.

The antenna of the construction of the embodiment of FIG. 4 having a rectangular cross section possesses all the features of the antenna of the construction of the preceding embodiment. All that was mentioned with respect to the construction of the proceeding embodiment is applicable here.

Besides the afore-mentioned features, the antenna construction of the second example has a feature in that the radiated electromagnetic wave is prevented from going around over to the back side, i.e. the side opposite the slotted side of the antenna, because the outer conductor is given a rectangular cross section and the slots are made in the broader face. In consequence, this antenna does not call for a special reflecting plate. Furthermore, this antenna can be as sembled of flat plates, so that its manufacture is exceedingly easy. Moreover, there will be less restriction as to the place where this antenna may be installed aboard a moving object.

FIG. 4(b) shows an example of a conversion connector to be installed at both ends of the coaxial line of this antenna. It is to be connected to a transmitter-receiver or to a nonrefective termination.

FIG. 5 shows a third example where the antenna shown in FIG. 4 has been greatly improved. It is a completely plate-form antenna made by mutually attaching tape-form metal conductors l3 and 14 and strip-form metal conductor 15 into one integral body with thermo-plastic insulating films '16 in-between.

Although this antenna has the form of a plate, it is of a coaxial type construction having 13 and 14 as outer conductors and 15 as an inner conductor. On the face 13 confronting the leaky coaxial cable are provided slots 10,, 10 in accordance with quite the same thinking as in the case of the examples shown in FIG. 3 and FIG. 4. Also in accordance with the same thinking as in the case of the afore-mentioned embodiments, the wavelength contraction ratio of this antenna is made to coincide with the wavelength contraction ratio of the leaky coaxial cable by adjusting the ratio of the insulating films 16 to the cross section of the antenna.

Electrically this antenna is not different from the antennas of the afore-mentioned two embodiments. It, therefore, possesses all the features of the afore-mentioned antennas. In addition, this antenna can be manufactured in the shape of a plate, so that it has flexibility which cannot be obtained with any other antenna. It is thus very advantageous with respect to handling in use and maintenance.

FIG. 6 shows the relationship between the positions of the antenna of this invention and the leaky coaxial cable. 1 denotes the leaky coaxial cable, 17 the transmitter or receiver, 18 the antenna of this invention, 19 the receiver or transmitter on board the moving object, and 20 the dummy load.

Stable vehicle communication is effected between a vehicle running along the cable 1 which carries an antenna 18 connected to the transmitter or receiver 19 and the receiver or transmitter 17 of a ground station via the wave coupling 2 and a leaky coaxial cable 1 on the ground.

As has been stated, the antenna of this invention has excellent features in that the construction of the antenna and the mechanism for its excitation are very simple because the system of coaxial progressive wave feeding is always employed. Also the radiation beams of the antenna and leaky coaxial cable are made to coincide at any desired frequency by making the slot structure and wavelength contraction ratio of the antenna coincide with those of the leaky coaxial cable. Stabilized com-. munication is thereby made possible, and the handling and maintenance of the antenna is made easy. Furthermore, when one wants to change the length of the antenna for example, when the antenna is made longer in order to decrease the coupling loss, the antenna shown in FIGS. 3 5 may be joined as a unit merely by jointing them longitudinally. Thus the antenna is useful for a very wide range of applications.

What we claim is:

the free space wavelength A being governed by the formula wherein 0 is the angle of directivity with respect to the cable axis, 1/ is the wave contraction ratio as defined by the ratio of the waveguide wavelength to the free space wavelength and n is an integer, and a substantially parallel leaky coaxial type vehicle antenna positioned for electromagnetic coupling with said leaky coaxial cable and having an outer conductor with an array of slots confronting said coaxial cable and which substan' tially coincides with the array of slots in said leaky coaxial cable with respect to configuration and the interval of periodicity of the slots, and a dielectric material interposed between the inner conductor and outer conductor of said antenna which is pre-adjustable to equalize the wavelength contraction ratio of said antenna to be in conformity with the wavelength contraction ratio of said cable.

2. The vehicle wireless communication system of claim 1 wherein the outer conductor of said coaxial type antenna is provided with a flat plate portion containing said array of slots which confronts said leaky coaxial cable.

3. The vehicle wireless communication system of claim 1 wherein the inner conductor of said coaxial type antenna is a metal strip and the outer conductor is of tubular construction having a rectangular cross section with a broader wall of said outer conductor containing the array of slots and confronting said leaky coaxial cable, and a dielectric material fixed on the inside wall of said outer conductor and supporting said inner conductor.

4. The vehicle wireless communication system of claim 1 wherein said inner conductor is a metal strip and said outer conductor consists of two metal strips overlying each other and in parallel with said inner conductor centrally sandwiched therebetween with dielectric material interposed between said outer metal strip with said inner conductor strip disposed therebetween, one of said outer metal strips containing said array of slots confronting said leaky coaxial cable. 

1. A vehicle wireless communication system comprising a leaky coaxial cable installed along a vehicle track and having an array of slots in its outer conductor which are located periodically along the cable axis at a slot pitch P/2 wherein P is approximately equal to one wave guide wavelength lambda g of an operating frequency, the free space wavelength lambda being governed by the formula theta cos 1 (1/ Nu - n lambda /P ), wherein theta is the angle of directivity with respect to the cable axis, Nu is the wave contraction ratio as defined by the ratio of the waveguide wavelength to the free space wavelength and n is an integer, and a substantially parallel leaky coaxial type vehicle antenna positioned for electromagnetic coupling with said leaky coaxial cable and having an outer conductor with an array of slots confronting said coaxial cable and which substantially coincides with the array of slots in said leaky coaxial cable with respect to configuration and the interval of periodicity of the slots, and a dielectric material interposed between the inner conductor and outer conductor of said antenna which is pre-adjustable to equalize the wavelength contraction ratio of said antenna to be in conformity with the wavelength contraction ratio of said cable.
 2. The vehicle wireless communication system of claim 1 wherein the outer conductor of said coaxial typE antenna is provided with a flat plate portion containing said array of slots which confronts said leaky coaxial cable.
 3. The vehicle wireless communication system of claim 1 wherein the inner conductor of said coaxial type antenna is a metal strip and the outer conductor is of tubular construction having a rectangular cross section with a broader wall of said outer conductor containing the array of slots and confronting said leaky coaxial cable, and a dielectric material fixed on the inside wall of said outer conductor and supporting said inner conductor.
 4. The vehicle wireless communication system of claim 1 wherein said inner conductor is a metal strip and said outer conductor consists of two metal strips overlying each other and in parallel with said inner conductor centrally sandwiched therebetween with dielectric material interposed between said outer metal strip with said inner conductor strip disposed therebetween, one of said outer metal strips containing said array of slots confronting said leaky coaxial cable. 